You are not allowed to blackmail someone into not posting, or into posting a certain number of times a day.
You are not allowed to restrict a player's ability to post, meaning you cannot force them to only post one specific message all day (but you can for example force them to post a certain message during the day).
You cannot demand more than two things at the same time.
You are not allowed to set conditions that imply a time limit.
You cannot restrict a player's ability to vote, apart from asking them not to vote another player.
You ARE allowed to force them to reveal their last will.
Your target is NOT allowed to reveal that they are blackmailed. They may soft-claim it however.
You CANNOT force a player to successfully lynch a target. You can ask them to push someone however.
You cannot blackmail someone more than twice in a row.
You cannot blackmail someone into claiming that they are currently blackmailed. You may however force them to say that they were, at one point, blackmailed.